Submitted to: Journal of New Seeds
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2005
Publication Date: 9/12/2006
Citation: Chung, S., Decker-Walters, D.S., Staub, J.E. 2006. Cultivar to wild population introgression in Cucurbita pepo subsp. ojiegra. Journal of New Seeds. 8:1-18. Interpretive Summary: The recent commercialization of numerous transgenic (plants that have genes that have been identified and modified) versions of crop (economically important plants) species (species in which genes from other species which have transgenes have been inserted into it) has provided many opportunities for U.S. agriculture that benefits both the farmer and consumer. However, there are potential ecological risks posed by the introduction of transgenes. Gene (located on chromosomes in the cell nucleus and made up of DNA) flow (i.e., movement of genes among plant populations) and rates of hybridization (cross fertilization between plants) between crops and wild relatives (found in rural habitats) indicate that genes are commonly introduced from crops into wild relatives. Spontaneous hybridization between transgenic cultivars and wild relatives occurs for 12 out of the 13 world's most important crops and their wild relative. Transgenic plants occur in squash crop species which carry virus resistance that have been obtained from other plants. It is important to identify the location of such wild species and assess their genetic nature (describe what types of genes they have). Such knowledge allows for the comparisions between wild and commercial species to determine the movement (through hybridization) between such squash species to assess changes between such populations when put in close proximity. Therefore an experiment was designed to assess the genetic nature of previously (1985) and newly (2000) collected wild squash species and commercial squash to determine if hybridization had occurred between them. Data suggest that in some cases genes were transferred between wild and commercial species and that, thus, there is a possibility of transfer of transgenes from commercial to wild plants. This information is important is developing guidelines for the commercialization of transgeneic squash and will allow the grower and the consumer to better beable to assess the socio-economic risks of having transgenes in production fields which are in close contact with wild squash populations.
Technical Abstract: Cultivar-to-wild population transgene flow occurs and can pose potential socio-ecological risks. In the U.S.A., transgenic commercial squash cultivars [i.e., Cucurbita pepo subspecies ovifera var. ovifera] are cultivated in close proximity to cross-compatible wild squash taxa (i.e., vars. ozarkana and texana) that are native to the Americas. This association provides a unique model for the assessment of cultivar-to-wild genetic contamination in this species. Thus, experiments were conducted using random amplified polymorphic DNA (RAPD) to estimate the qualitative genetic compositions of wild populations of C. pepo and evaluate such genetic variation within the contexts of naturally-occuring geographically-based divergence as well as introgression of alleles from cultivated stands into free-living populations. Free-living populations of C. pepo from the Ozark Plateau (southern Missouri, northwestern Arkansas, northeastern Oklahoma), Mississippi, Texas, Illinois, Kentucky, and Louisiana were examined using 21 RAPD primers (23 discriminatory bands). Banding morphotypes were useful for discriminating populations. It appears that C. pepo populations in southeastern Texas and the Ozark Plateau are relatively homogeneous and the least genetically contaminated by introgression from cultivars, and are thus the most representative genetic samples of var. texana and var. ozarkana, respectively. The genetic compositions of accessions from some free-living populations, particularly in Illinois and Kentucky, suggests that squash, pumpkin, and ornamental gourd farming continue to be sources of genetic contamination for nearby wild populations. Thus, gene flow from transgenic cultivars to wild populations can occur, possibly resulting in changes in the genetic structure of populations, necessitating the judicial appraisal of the risks associated with such events.